In this lesson, you will learn how to safely deploy updated kernel binaries and device tree blobs to your target storage media to apply hardware configuration changes.
When you modify your Device Tree source (.dts) or recompile your Linux kernel, you produce new binaries—typically zImage (or uImage) and .dtb files. Simply compiling them isn't enough; you must transition these files from your build machine to the non-volatile storage (like eMMC, SD card, or NAND flash) where the bootloader expects to find them.
Safe Deployment Strategies
Updating these files directly on a live system carries the risk of a "bricked" device if the power fails mid-write. To update safely, follow these steps:
- Transfer: Move the files to the target using
scp,tftp, or an external storage medium. - Verification: Always verify the integrity of the transfer using a checksum (e.g.,
md5sum). - Atomic Replacement: When writing to flash, ensure your update mechanism is robust. If your boot partition is mounted, copy the new file to a temporary name first, then rename it (or use
sync) to ensure the filesystem metadata is committed.
For systems using U-Boot, you often store these files in a specific partition (e.g., the boot partition). If your boot partition is mounted at /boot, a manual update usually looks like this:
# Verify integrity on the target
md5sum zImage.new
# Copy to the active boot path
cp zImage.new /boot/zImage
cp board-revision-a.dtb /boot/board.dtb
# Ensure buffers are flushed to physical media
sync
Handling Configuration Changes
When you update the Device Tree, you are altering the underlying hardware description—such as changing a GPIO pin mode or I2C clock speed. Because the bootloader reads the .dtb file during the boot sequence, the changes won't take effect until the next reset. Before rebooting, ensure your uEnv.txt or U-Boot environment variables correctly point to the new filename if you have renamed it.
Always keep a known-good backup of your previous kernel and DTB on the target. If the new configuration causes a kernel panic, you can drop into the U-Boot console and manually load the backup files to restore functionality.
Key Takeaway: Updating your kernel and device tree requires a reliable transfer, a verified write to persistent storage, and a forced sync to prevent data corruption during the transition to the new hardware configuration.